US 2006/0120507 A1 discloses such an x-ray diagnostic device for executing the method for angiography, which is shown for example in FIG. 1, which features a C-arm 2 supported to allow it to rotate on a stand 1, at the ends of which an x-ray radiation source, for example an x-ray emitter 3, and an x-ray image detector 4 are arranged.
The x-ray image detector 4 can be a rectangular or square flat semiconductor detector, which is preferably made of amorphous silicon (a-Si).
Located in the optical path of the x-ray emitter 3 is a patient support table 5 for recording images for example of a heart of a patient to be examined. Connected to the x-ray diagnostic device is an imaging system 6 which receives and processes the image signals of the x-ray image detector 4. The x-ray images can then be viewed on a monitor 7.
During recording of such 2D data x-ray images are frequently produced which have a very high amount of noise and in which the signal-to-noise ratio is thus also bad. This can make diagnosis more difficult.
If 3D data sets are to be created, the rotatably-supported C-arm 2 with x-ray source 3 and x-ray detector 4 is turned, so that, as shown schematically in FIG. 2 looking down on the axis of rotation, the x-ray source 3 shown in this diagram by its beam focus 3 as well as the x-ray image detector 4 move around an object 9 to be examined on a planetary track 8. The planetary track 8 can be followed completely or partly for creating a 3D data set.
The object 9 to be examined can for example be the body of an animal or a human being, but can also be a phantom body.
The x-ray source 3 emits a ray bundle 10 emanating from the ray focus of its radiographic source, which hits the x-ray image detector 4.
The x-ray source 3 and the x-ray image detector 4 thus each circulate around the object 5, so that the x-ray source 3 and the x-ray image detector 4 lie on opposite sides of the object 9 in relation to each other.
In normal radiography or fluoroscopy using such an x-ray diagnostic device the medical 2D data of the x-ray image detector 4 will be buffered in the imaging system 6 if necessary and subsequently reproduced on the monitor 7.
FIG. 3 now shows the known execution sequence for recording 3D-data which is created by means of an x-ray device 11 described in FIGS. 1 and 2. The raw data 12 is fed to a reconstruction 13, which computes from it the volume data set or 3D data set 14.
In the creation of such 3D data, the reconstruction can be adversely affected as a result of noise in the raw data, which leads to a reduction in the ability to detect contrasts and structures in the 3D data set.
In a reconstruction of the 3D data, said data comprises a data set containing density information of the location (x, y, z) for example. This density information can now contain a noise component which reduces the 3D image quality.
The only option available to the doctor for increasing the signal-to-noise ratio (S/N ratio) and thus the image quality is to increase the dose, but this results in both the patient and the doctor being subjected to a higher exposure to radiation. There are also statutory regulations restricting the maximum dose.
Although the S/N ratio can be improved by a smoothing filter, for example Crispyl, which finds edges in the image and smoothes the image along these edges, a meaningful noise reduction is not guaranteed by this.